This invention relates generally to dock levelers and, more particularly, to extendible dock levelers.
Dock levelers are typically installed in the loading dock areas of factories, warehouses and similar facilities. In use, a dock leveler serves primarily as a ramp or bridge that extends from the loading dock area of the factory or warehouse into the rear end of a truck trailer. Known dock levelers include hydraulically actuated, extendible levelers wherein a forward section of a movable ramp can be extended or retracted to vary the effective length of the ramp.
When a dock leveler is placed into a track trailer, the amount of "lip purchase" (i.e., the amount by which the dock leveler extends into and overlaps the edge of the mack trailer) is an important consideration. Too little lip purchase can create an unsafe condition. Too much lip purchase can result in physical damage to both the mack trailer and the dock leveler.
In prior dock levelers, the appropriate amount of lip purchase was estimated by the operator, assuming the operator gave conscious thought to the matter at all. Frequently, the resulting amount of lip purchase was not something arrived at after careful thought and consideration but, rather, was determined intuitively on the basis of what "looked right." Although such an intuitive approach was effective when skilled and experienced operators were available, a potential for mishap existed when careless or inattentive operators were involved.
Another potential for mishap occurred when the forward section of an extendible leveler was forced backwardly toward the rear section of the leveler by the drive wheels of a forklift or other vehicle. Such unintended movement shortened the overall effective length of the ramp and reduced the resulting lip purchase. Although the lip purchase might have been acceptable when initially set, an unacceptably small lip purchase might have resulted following such unintended movement.
Examples of hydraulically actuated, extendible dock levelers are shown in the following U.S. patents:
U.S. Pat. No. Inventor Issue Date
4,551,877 Alten Nov. 12, 1985
4,224,709 Alten Sep. 30, 1980
3,235,895 Wallace, et al. Feb. 22, 1966
3,179,968 Lambert Apr. 27, 1965
3,175,238 Pennington Mar. 30, 1965
3,167,796 Layne Feb. 2, 1965
2,689,965 Fenton Sep. 28, 1954
In each of the systems shown in these patents the amount of lip purchase was left to the operator's discretion, and no structure was provided for carefully setting or maintaining the amount of lip purchase.